1. Field of the Invention
The present invention relates to a system for cleaning the interior of pipes. In particular, the invention comprises a system for cleaning deposits from the walls of pipelines or other pipe systems.
2. Background
Pipeline systems are utilized throughout the world to transport petroleum products, water, municipal wastes, chemical slurries and other fluids. During the transport of these materials there is often a build-up of materials, including paraffin, calcium and silica, on the inner wall of the pipeline. One of the materials which builds up most frequently in petroleum pipelines is paraffin. As the deposits of paraffin and/or other materials increase, the bore of the pipeline or other piping through which the fluid flows becomes restricted, resulting in a loss of fluid flow. or an increase in energy required to maintain the fluid flow.
Pipeline pigs have been used for many years to remove deposits from the inside of pipes. A pipeline pig comprises a body having an outer circumference closely matching the inner circumference of the pipe. The pig is inserted in the pipe and is forced through the pipe by fluid pressure. As the pig travels through the pipe it scrapes the deposits from the interior wall of the pipe and transports these deposits along the pipeline. The pig needs to be substantially rigid in order to scrape deposits form the wall of the pipe, but the pig also needs to be somewhat compressible in order to pass by restrictions in the internal pipe cross-section or obstructions that may be present in the pipe. Typically the exterior surface of a pipeline pig is formed from a plastic material, such as polyurethane. A disadvantage of these pigs is that the build-up of paraffin or other material inside the pipe may be so rigid that the pig will compress and ride over the build-up, which results in insufficient cleaning. Normally, the fluid pressure for propelling the pig through the pipe is supplied by water or other liquids which are injected into the pipe at high pressure following insertion of the pig into the pipe. It is also known to the prior art to initially inject high pressure water behind the pig and to then discontinue the injection of water and inject only a gas to complete the propulsion of the pig through the pipe.
Fluids have been used in conjunction with pipeline pigs for certain cleaning purposes. U.S. Pat. No. 5,795,402, which issued on Aug. 18, 1998 to Hargett, Sr. et al., discloses a pipeline pig having a plurality of nozzles positioned on the forward end of the pig for allowing fluid under pressure to flow from the nozzles onto the inner wall of the pipeline. When the pig encounters an obstruction which hinders forward movement, pressure is increased sufficiently to move a valving member to the open position which allows fluid under pressure to spray from the nozzles to provide sufficient heating to melt the paraffin or other build-up. In one embodiment of the system disclosed in U.S. Pat. No. 5,795,402, a first chemical compound, preferably hydrochloric acid, is positioned forward of the pig, and a second chemical compound, preferably anhydrous ammonia, is positioned to the rear of the pig. When an obstruction is encountered, fluid in a chamber 36 reaches a certain pressure and a sealing member 74 within a pressure valve 70 moves forward, allowing fluid to flow into the nose cone of the pig and out the nozzles. Upon this happening, the anhydrous ammonia encountering the hydraulic acid will create an exothermic reaction and the resulting heat will melt the built up paraffin. When the paraffin has been sufficiently softened the pig is then able to move forward under pressure applied to the rear of the pig. In another embodiment disclosed in U.S. Pat. No. 5,795,402, the water which is used to push the pig is heated to a very high temperature, above the temperature for melting paraffin. When the pig reaches an obstruction of paraffin, valve member 70 is activated, which allows the super heated water to flow into the nose cone of the pig and out of the nozzles under pressure to begin melting or softening the wax build-up. As the pig moves forward, pressure is reduced and the valve 70 closes, and the pressure of the water simply moves the pig along the pipeline until it encounters another obstruction.
U.S. Pat. No. 4,498,932, which issued on Feb. 12, 1985 to Kruka, discloses a pipeline pig having a restricted fluid bypass channel which serves to bring fluid from the back of the pig to its front. This fluid agitates and suspends discrete solids such as sand or rust, or commingles with paraffinic and asphaltic deposits which have been scraped from the pipe wall by the pig as it moves through the line, to prevent the buildup of a solid bed or plug of sufficient thickness or viscosity in front of the pig so as to cause the pig to partially collapse and ride over it or to become stuck. The passageway through the pig is terminated by nozzles or orifices which are fastened to the pig. The orifices are chosen to give a desired flow rate and pressure drop across the pig. In this disclosure, fluid flow through the nozzle is intended to agitate and suspend discrete solids such as sand or rust, or to commingle with scraped paraffinic and asphaltic deposits which have been scraped from the pipe walls by the pig. There is no suggestion, however, of blasting the paraffinic or asphaltic deposits from the pipeline wall with the force of the fluid stream emanating from the nozzles.
U.S. Pat. No. 5,875,803, which issued on Mar. 2, 1999 to Leitko et al., shows a conduit cleaning pig which includes a sealing means for preventing a significant flow of fluids from the upstream side of the pig to the downstream side of the pig between the conduit and the pig. The pig includes a rotating element connected to the downstream side of the seal means and a plurality of nozzles connected to the rotating element, each nozzle defining a flow path. The flowpath through the nozzles is in communication with a channel from the upstream side of the seal. The flowpaths through the nozzles are aligned in part tangentially to the cylinder around the central axis of the pig and aligned in part toward the inside wall of the conduit. Liquid jets of the fluid transporting the pig down the conduit impinge on the conduit in front of the pig and remove deposits from the wall of the conduit. The fluid passing through the pig then transports the solids through the conduit ahead of the pig.
Another system which utilizes a fluid flow to assist in cleaning the inside of a pipe is disclosed in U.S. Pat. No. 5,444,887, which issued on Aug. 29, 1995 to Rufolo. This patent discloses a cleaning device for removing shellfish obstructions from an interior surface of an underwater intake pipe. The system includes a member having a blade-like front surface and a blade-like rear surface for scraping foreign matter from the inside surface of a conduit. The cleaning device also includes fluid jet nozzles for producing a jet stream used in transferring the foreign matter along the pipe""s floor. While the system uses a fluid stream to transfer foreign matter scraped from the pipe wall by the blades, there is no suggestion of using the fluid stream to blast the foreign matter from the pipe walls.
Hydro blasting is another method which has been utilized to clean the inside of pipes. The hydro blasting process for cleaning the interior of a pipe typically employs a line mole attached to the end of a hose, which is inserted into the pipe, such as the system illustrated in a brochure from Euro Aqua Drill, of Webster, Tex. High pressure water is supplied to the line mole through the hose, which will extend to the line mole from a high pressure water pump on the exterior of the pipe. The line mole includes nozzles through which water is ejected at a high velocity as the line mole travels through the pipe. Some of these nozzles face in a diagonally forward direction or perpendicular direction with respect to the axis of the pipe, and the water which is ejected through these nozzles blasts the paraffin or other deposit from the pipe wall. Other nozzles face in the reverse or diagonally reverse direction, and sufficient water or other fluid is propelled in the reverse direction to create a jet propulsion to propel the line mole, along with the attached hose, into the pipe. A hose is unreeled from a rotating device operated by an air motor driven by an air compressor. As the line mole travels into the pipe, it will have to drag a greater and greater length of the hose, and a correspondingly greater and greater weight, and the distance the line mole can travel into the pipe is limited. Accordingly, the length of pipe that can be cleaned with this process is limited.
A xe2x80x9chydrokineticxe2x80x9d process for cleaning relatively short pipes is presented in a brochure from AIMM Technologies, Inc. This process is said to be based on resonant frequencyxe2x80x94the process of inducing a frequency vibration into the water stream. The brochure states that: xe2x80x9cAn oscillating water stream is transmitted into the tubc or pipe which is to be cleaned. The resonance is then transferred to both the tube and to the fouling material, which will vibrate at different frequencies because they are of different densities. The separate vibrations cause a break in the cohesion between the fouling material and the tube wall and fouling material flushes from the pipe via the water stream.xe2x80x9d The hydrokinetic method is implemented by injecting into the pipe entrance an oscillating water stream interspersed with air. Because the fluids are injected into the pipe at the pipe entrance the length of pipe than can be cleaned with this process is limited.
A long felt need remains, however, for a more efficient system for cleaning the inside of pipelines and other piping systems; a need that is met by the invention disclosed herein.
In a first embodiment the invention comprises a method for cleaning deposits from the interior of a pipe in which a pig is propelled through the pipe by pressure from a fluid mixture of at least one liquid and at least one gas applied to the pig from the rear end of the pig. A portion of the fluid mixture is conducted from the rear of the pig to at least one nozzle on the forward end of said pig and is propelled through the nozzle to clean the deposits from the interior of the pipe. In a particular implementation, the fluid mixture cleans the interior of said pipe simultaneously by blasting and by the generation of vibrations of different frequencies in the pipe and in the deposits.
In another embodiment the invention comprises a method of determining a maximum pressure that may be safely used for cleaning the interior of a pipe. The wall thickness of the pipe, the yield point of the pipe material in new condition, the number of months the pipe has been in use, and the outside diameter of the pipe are determined and the following relationship, (2t)(myp)/0.75(o.d.), is utilized to determine such maximum pressure, wherein t is equal to the pipe wall thickness, myp is equal to the yield point of the pipe material in new condition reduced by 0.1 percent per month for each month the pipe has been in use, and o.d. is equal to the outside diameter of the pipe.
In yet another embodiment the invention comprises a pig for cleaning the inside of a pipe. The pig includes a flexible fluid conduit having a rear end and a forward end, a first cylindrical member having a surface against which fluid pressure may be applied to propel the pig through the pipe mounted on the conduit at substantially the rear end of the conduit and a second cylindrical member having a surface adapted to form a substantially sealing engagement with the interior wall of the pipe mounted on the conduit at substantially the forward end of the conduit. A plurality of nozzles are mounted in fluid communication with the fluid conduit substantially at the forward end of the conduit through which fluid flowing from the rear end of the conduit may be propelled against the pipe surface for cleaning the pipe.